A waveguide bend used in a high-frequency transmission line has been known. The waveguide bend includes a bend which changes a propagation direction of a radio wave.
The waveguide bend is generally manufactured by assembling a plurality of metal pieces. In some cases where the plurality of metal pieces is assembled, an assembling operation may be complicated, and thus, it may be difficult to improve manufacturability.
If a tube width of a part of the waveguide bend is set to be narrow in order to reduce an undesired wave, to reduce thermal noise, or to achieve another purpose, it may be difficult to achieve impedance matching. If a sectional shape of the waveguide bend has manufacturing limitations, it may be difficult to achieve impedance matching in some cases.